<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>is_function</title>
<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../../index.html" title="Chapter 1. Boost.TypeTraits">
<link rel="up" href="../reference.html" title="Alphabetical Reference">
<link rel="prev" href="is_floating_point.html" title="is_floating_point">
<link rel="next" href="is_fundamental.html" title="is_fundamental">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
<td align="center"><a href="../../../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="is_floating_point.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="is_fundamental.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.reference.is_function"></a><a class="link" href="is_function.html" title="is_function">is_function</a>
</h3></div></div></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_function</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span>
</pre>
<p>
        <span class="bold"><strong>Inherits:</strong></span> If T is a (possibly cv-qualified)
        function type then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
        otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
        Note that this template does not detect <span class="emphasis"><em>pointers to functions</em></span>,
        or <span class="emphasis"><em>references to functions</em></span>, these are detected by <a class="link" href="is_pointer.html" title="is_pointer">is_pointer</a> and <a class="link" href="is_reference.html" title="is_reference">is_reference</a> respectively:
      </p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">f1</span><span class="special">();</span>      <span class="comment">// f1 is of function type.</span>
<span class="keyword">typedef</span> <span class="keyword">int</span> <span class="special">(*</span><span class="identifier">f2</span><span class="special">)();</span>   <span class="comment">// f2 is a pointer to a function.</span>
<span class="keyword">typedef</span> <span class="keyword">int</span> <span class="special">(&amp;</span><span class="identifier">f3</span><span class="special">)();</span>   <span class="comment">// f3 is a reference to a function.</span>
</pre>
<p>
        <span class="bold"><strong>C++ Standard Reference:</strong></span> 3.9.2p1 and 8.3.5.
      </p>
<p>
        <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers
        are supported by this trait.
      </p>
<p>
        <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
        <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_function</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
        or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
      </p>
<p>
        <span class="bold"><strong>Examples:</strong></span>
      </p>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)&gt;</span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">type</span></code> is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(*)(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>false</em></span>: the argument in this case
          is a pointer type, not a function type.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(&amp;)(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>false</em></span>: the argument in this case
          is a reference to a function, not a function type.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="keyword">long</span> <span class="special">(</span><span class="identifier">MyClass</span><span class="special">::*)(</span><span class="keyword">double</span><span class="special">,</span> <span class="keyword">int</span><span class="special">)&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>false</em></span>: the argument in this case
          is a pointer to a member function.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_function</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code> is the type <code class="computeroutput"><span class="keyword">bool</span></code>.
        </p></blockquote></div>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top">
<p>
          Don't confuse function-types with pointers to functions:
        </p>
<p>
          <code class="computeroutput"><span class="keyword">typedef</span> <span class="keyword">int</span>
          <span class="identifier">f</span><span class="special">(</span><span class="keyword">double</span><span class="special">);</span></code>
        </p>
<p>
          defines a function type,
        </p>
<p>
          <code class="computeroutput"><span class="identifier">f</span> <span class="identifier">foo</span><span class="special">;</span></code>
        </p>
<p>
          declares a prototype for a function of type <code class="computeroutput"><span class="identifier">f</span></code>,
        </p>
<p>
          <code class="computeroutput"><span class="identifier">f</span><span class="special">*</span>
          <span class="identifier">pf</span> <span class="special">=</span>
          <span class="identifier">foo</span><span class="special">;</span></code>
        </p>
<p>
          <code class="computeroutput"><span class="identifier">f</span><span class="special">&amp;</span>
          <span class="identifier">fr</span> <span class="special">=</span>
          <span class="identifier">foo</span><span class="special">;</span></code>
        </p>
<p>
          declares a pointer and a reference to the function <code class="computeroutput"><span class="identifier">foo</span></code>.
        </p>
<p>
          If you want to detect whether some type is a pointer-to-function then use:
        </p>
<p>
          <code class="computeroutput"><a class="link" href="is_function.html" title="is_function">is_function</a><span class="special">&lt;</span><a class="link" href="remove_pointer.html" title="remove_pointer">remove_pointer</a><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">type</span><span class="special">&gt;::</span><span class="identifier">value</span>
          <span class="special">&amp;&amp;</span> <a class="link" href="is_pointer.html" title="is_pointer">is_pointer</a><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value</span></code>
        </p>
<p>
          or for pointers to member functions you can just use <a class="link" href="is_member_function_pointer.html" title="is_member_function_pointer">is_member_function_pointer</a>
          directly.
        </p>
</td></tr>
</table></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams,
      Frederic Bron, Steve Cleary, Beman Dawes, Glen Fernandes, Aleksey Gurtovoy,
      Howard Hinnant, Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander
      Nasonov, Thorsten Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert
      Stewart and Steven Watanabe<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="is_floating_point.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="is_fundamental.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
